Hi Jiri, On Thu, Aug 12, 2010 at 03:11:03PM +0800, Jiri Slaby wrote: > Hi Wu, > > maybe you've already sent a backported version of e31f3698cd34 for > 2.6.34 stable. If you haven't yet, I'm attaching my version in case you > don't want to duplicate work. There is a change where lumpy_reclaim is > passed as a parameter, since struct scan_control doesn't contain that > yet in 2.6.34. This patch for -stable looks good, thank you! Greg, this patch has received pretty positive feedbacks from some users. (others feel no changes: there are more sources of responsiveness stalls) KOSAKI and me think it's important and safe enough for -stable kernels. The patch looks large, however it's mainly cleanups. The real change is merely about raising (DEF_PRIORITY-2) to (DEF_PRIORITY/3) in the test condition. Thanks, Fengguang > From e31f3698cd3499e676f6b0ea12e3528f569c4fa3 Mon Sep 17 00:00:00 2001 > From: Wu Fengguang <fengguang.wu@xxxxxxxxx> > Date: Mon, 9 Aug 2010 17:20:01 -0700 > Subject: vmscan: raise the bar to PAGEOUT_IO_SYNC stalls > > Fix "system goes unresponsive under memory pressure and lots of > dirty/writeback pages" bug. > > http://lkml.org/lkml/2010/4/4/86 > > In the above thread, Andreas Mohr described that > > Invoking any command locked up for minutes (note that I'm > talking about attempted additional I/O to the _other_, > _unaffected_ main system HDD - such as loading some shell > binaries -, NOT the external SSD18M!!). > > This happens when the two conditions are both meet: > - under memory pressure > - writing heavily to a slow device > > OOM also happens in Andreas' system. The OOM trace shows that 3 processes > are stuck in wait_on_page_writeback() in the direct reclaim path. One in > do_fork() and the other two in unix_stream_sendmsg(). They are blocked on > this condition: > > (sc->order && priority < DEF_PRIORITY - 2) > > which was introduced in commit 78dc583d (vmscan: low order lumpy reclaim > also should use PAGEOUT_IO_SYNC) one year ago. That condition may be too > permissive. In Andreas' case, 512MB/1024 = 512KB. If the direct reclaim > for the order-1 fork() allocation runs into a range of 512KB > hard-to-reclaim LRU pages, it will be stalled. > > It's a severe problem in three ways. > > Firstly, it can easily happen in daily desktop usage. vmscan priority can > easily go below (DEF_PRIORITY - 2) on _local_ memory pressure. Even if > the system has 50% globally reclaimable pages, it still has good > opportunity to have 0.1% sized hard-to-reclaim ranges. For example, a > simple dd can easily create a big range (up to 20%) of dirty pages in the > LRU lists. And order-1 to order-3 allocations are more than common with > SLUB. Try "grep -v '1 :' /proc/slabinfo" to get the list of high order > slab caches. For example, the order-1 radix_tree_node slab cache may > stall applications at swap-in time; the order-3 inode cache on most > filesystems may stall applications when trying to read some file; the > order-2 proc_inode_cache may stall applications when trying to open a > /proc file. > > Secondly, once triggered, it will stall unrelated processes (not doing IO > at all) in the system. This "one slow USB device stalls the whole system" > avalanching effect is very bad. > > Thirdly, once stalled, the stall time could be intolerable long for the > users. When there are 20MB queued writeback pages and USB 1.1 is writing > them in 1MB/s, wait_on_page_writeback() will stuck for up to 20 seconds. > Not to mention it may be called multiple times. > > So raise the bar to only enable PAGEOUT_IO_SYNC when priority goes below > DEF_PRIORITY/3, or 6.25% LRU size. As the default dirty throttle ratio is > 20%, it will hardly be triggered by pure dirty pages. We'd better treat > PAGEOUT_IO_SYNC as some last resort workaround -- its stall time is so > uncomfortably long (easily goes beyond 1s). > > The bar is only raised for (order < PAGE_ALLOC_COSTLY_ORDER) allocations, > which are easy to satisfy in 1TB memory boxes. So, although 6.25% of > memory could be an awful lot of pages to scan on a system with 1TB of > memory, it won't really have to busy scan that much. > > Andreas tested an older version of this patch and reported that it mostly > fixed his problem. Mel Gorman helped improve it and KOSAKI Motohiro will > fix it further in the next patch. > > Reported-by: Andreas Mohr <andi@xxxxxxxx> > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Signed-off-by: Mel Gorman <mel@xxxxxxxxx> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> > --- > mm/vmscan.c | 53 +++++++++++++++++++++++++++++++++++++++++++++-------- > 1 file changed, 45 insertions(+), 8 deletions(-) > > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1118,6 +1118,48 @@ static int too_many_isolated(struct zone > } > > /* > + * Returns true if the caller should wait to clean dirty/writeback pages. > + * > + * If we are direct reclaiming for contiguous pages and we do not reclaim > + * everything in the list, try again and wait for writeback IO to complete. > + * This will stall high-order allocations noticeably. Only do that when really > + * need to free the pages under high memory pressure. > + */ > +static inline bool should_reclaim_stall(unsigned long nr_taken, > + unsigned long nr_freed, > + int priority, > + int lumpy_reclaim, > + struct scan_control *sc) > +{ > + int lumpy_stall_priority; > + > + /* kswapd should not stall on sync IO */ > + if (current_is_kswapd()) > + return false; > + > + /* Only stall on lumpy reclaim */ > + if (!lumpy_reclaim) > + return false; > + > + /* If we have relaimed everything on the isolated list, no stall */ > + if (nr_freed == nr_taken) > + return false; > + > + /* > + * For high-order allocations, there are two stall thresholds. > + * High-cost allocations stall immediately where as lower > + * order allocations such as stacks require the scanning > + * priority to be much higher before stalling. > + */ > + if (sc->order > PAGE_ALLOC_COSTLY_ORDER) > + lumpy_stall_priority = DEF_PRIORITY; > + else > + lumpy_stall_priority = DEF_PRIORITY / 3; > + > + return priority <= lumpy_stall_priority; > +} > + > +/* > * shrink_inactive_list() is a helper for shrink_zone(). It returns the number > * of reclaimed pages > */ > @@ -1209,14 +1251,9 @@ static unsigned long shrink_inactive_lis > nr_scanned += nr_scan; > nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC); > > - /* > - * If we are direct reclaiming for contiguous pages and we do > - * not reclaim everything in the list, try again and wait > - * for IO to complete. This will stall high-order allocations > - * but that should be acceptable to the caller > - */ > - if (nr_freed < nr_taken && !current_is_kswapd() && > - lumpy_reclaim) { > + /* Check if we should syncronously wait for writeback */ > + if (should_reclaim_stall(nr_taken, nr_freed, priority, > + lumpy_reclaim, sc)) { > congestion_wait(BLK_RW_ASYNC, HZ/10); > > /* -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>